As an infrared detector, there has been known a pyroelectric infrared detector, incorporated in a gas analyzer, a radiation thermometer, a flame detector, an intruder alarm or the like (e.g., see JP 3247813 B2: hereinafter, referred to as “Document 1”).
In Document 1, a pyroelectric infrared detector 200 that has a configuration shown in FIG. 72 is described. The pyroelectric infrared detector 200 includes a case 201, an infrared transmission window 202, a stem 203, a circuit substrate 204, a pyroelectric member 205, and a spacer 206. In addition, two electrodes 207 and 208 that constitute an electrode portion are provided on both of top and bottom surfaces of the pyroelectric member 205, respectively.
The pyroelectric infrared detector 200 is a dual type, and the two electrodes 207 and 208 are connected in series so as to have a reverse polarity to each other.
The pyroelectric infrared detector 200 is configured such that only one electrode 207 of the two electrodes 207 and 208 faces the infrared transmission window 202, and accordingly, infrared light 213 passing through the infrared transmission window 202 is incident on the one electrode 207, but infrared light is not incident on the other electrode 208. Hereinafter, the one electrode 207 and the other electrode 208 are respectively referred to as an “electrode for receiving infrared light” 207 and an “electrode for compensating temperature” 208.
In the pyroelectric infrared detector 200, a thickness of the electrode for compensating temperature 208 is set to be larger that of the electrode for receiving infrared light 207, so that an optical absorption coefficient in an infrared region of the electrode for compensating temperature 208 is less than that of the electrode for receiving infrared light 207. In the pyroelectric infrared detector 200, for example, the electrode for receiving infrared light 207 has the thickness of 100 Å, and the electrode for compensating temperature 208 has the thickness of 1000 Å. Accordingly, in the pyroelectric infrared detector 200, the optical absorption coefficient in the infrared region of the electrode for compensating temperature 208 is set to half of that of the electrode for receiving infrared light 207. Therefore, even if infrared light is incident on the electrode for compensating temperature 208 due to crosstalk, a signal is hardly output from the electrode for compensating temperature 208, and sensitivity of the pyroelectric infrared detector 200 is accordingly improved.